Bazza Posted February 24, 2021 Report Share Posted February 24, 2021 If this has been asked before - apologies. The overdrive has never worked on my 1974 MKIV Spitfire. Today I took the plunge and removed the gearbox tunnel. Does anyone have a wiring diagram the only one I have includes a relay. From the switch in the gear-lever one wires goes to earth. The other switch wire goes to the solenoid. A wire then goes to the gearbox isolator switch from the solenoid. There is an wire that comes from the engine bay (wired into the ballast resistor) which is attached to the gearbox isolator switch. Is this correct? please see pictures attached Thanks Barry Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 24, 2021 Report Share Posted February 24, 2021 this is from steves online manuals page 2.307 but looking at you pic the solenoid appears on the LH side so its a J type not a D type ??? the only change is a D type (sol on the RH side ) must have a relay the J type does not , but which ever the feed needs to be from a white ignition controlled wire certainly not off the ignition ballast coil wire the dropped voltage wont help the OD at all as the wiring goes up the hollow gear stick i would take a carefull lookas here it gets cooked and chafed try to get some silicon sheathed wire its more pliable/less chaffed and heat proofed Pete Link to comment Share on other sites More sharing options...
NonMember Posted February 24, 2021 Report Share Posted February 24, 2021 No, your wiring isn't correct. Since a Mk4 should have a D type, which would need a solenoid as per Pete's diagram, my suspicion is that the PO who installed the J type had not the first clue about electrics and made it up (wrongly) as he went. It's possible it worked but it's not how a J type should be wired. When you say that the green/white wire from the inhibitor "comes from the engine bay (wired into the ballast resistor)", which end of the ballast resistor? It should be either a straight green wire from the fused ignition-switched supply, or a white wire from the ignition switch via an extra fuse. The factory would have used green because there's already a green wire down there for the reverse lights (although I can't see it in your photos). Link to comment Share on other sites More sharing options...
DanMi Posted February 24, 2021 Report Share Posted February 24, 2021 very late mk4 had a J type. Your wiring clearly isn't factory but should function so long as it goes to the 12v side of the ballast resistor. I would put it in 4th gear with ignition on and engage od you should hear the solenoid click. Link to comment Share on other sites More sharing options...
Colin Lindsay Posted February 24, 2021 Report Share Posted February 24, 2021 23 minutes ago, NonMember said: The factory would have used green because there's already a green wire down there for the reverse lights (although I can't see it in your photos). For the J-type, power is taken off the reversing light circuit; think of it as a loop beginning at the switch and ending at the solenoid, with two breaks - the manual switch, and the inhibitor switch. It needs both breaks completed ie gearstick in the correct position for the operating cam to depress the inhibitor switch, and the manual switch closed. That just makes one large loop into which power is fed from the reversing light circuit. I have no relay on mine. If you look at the photo of mine, rewired in non-original light green and red due to prolonged electrical faults late last year, you can see the taped black wire from the reversing circuit coming in from the left. The green wire splits at the switch - centre of photo - which is where power gets in; the other switch terminal, here in red, goes off to the manual switch through that protective plastic sheathing. From there is comes back to the solenoid, and is then earthed. The two green wires to the right are the reversing switch. It's quite a simple circuit. Link to comment Share on other sites More sharing options...
Bazza Posted February 24, 2021 Author Report Share Posted February 24, 2021 23 minutes ago, NonMember said: No, your wiring isn't correct. Since a Mk4 should have a D type, which would need a solenoid as per Pete's diagram, my suspicion is that the PO who installed the J type had not the first clue about electrics and made it up (wrongly) as he went. It's possible it worked but it's not how a J type should be wired. When you say that the green/white wire from the inhibitor "comes from the engine bay (wired into the ballast resistor)", which end of the ballast resistor? It should be either a straight green wire from the fused ignition-switched supply, or a white wire from the ignition switch via an extra fuse. The factory would have used green because there's already a green wire down there for the reverse lights (although I can't see it in your photos). Hi Thanks for your reply. Please see my reply to Pete. There are some green wires and red bundled together see photo. thanks Barry Link to comment Share on other sites More sharing options...
Bazza Posted February 24, 2021 Author Report Share Posted February 24, 2021 11 minutes ago, Colin Lindsay said: For the J-type, power is taken off the reversing light circuit; think of it as a loop beginning at the switch and ending at the solenoid, with two breaks - the manual switch, and the inhibitor switch. It needs both breaks completed ie gearstick in the correct position for the operating cam to depress the inhibitor switch, and the manual switch closed. That just makes one large loop into which power is fed from the reversing light circuit. I have no relay on mine. If you look at the photo of mine, rewired in non-original light green and red due to prolonged electrical faults late last year, you can see the taped black wire from the reversing circuit coming in from the left. The green wire splits at the switch - centre of photo - which is where power gets in; the other switch terminal, here in red, goes off to the manual switch through that protective plastic sheathing. From there is comes back to the solenoid, and is then earthed. The two green wires to the right are the reversing switch. It's quite a simple circuit. Hi Colin Thank you for your reply. So you’ve used the feed from the reversing light circuit to power the solenoid etc? Barry Link to comment Share on other sites More sharing options...
Colin Lindsay Posted February 24, 2021 Report Share Posted February 24, 2021 The green wire to the reversing light branches at the spade connector on the O/D inhibitor switch; one side into the reversing light switch and the other to the O/D inhibitor switch. Both circuits only work when the gearlever is in the correct place to activate the relevant switch so they can't be on at the same time. Once the inhibitor switch is tripped power will get to the manual switch, but no further until it too is switched on, which completes the power to the solenoid; it just leaves the solenoid to earth. Link to comment Share on other sites More sharing options...
NonMember Posted February 24, 2021 Report Share Posted February 24, 2021 1 hour ago, Bazza said: Please see my reply to Pete. I can't see any reply to Pete... 58 minutes ago, Bazza said: So you’ve used the feed from the reversing light circuit to power the solenoid etc? Yes, that is what the factory did when they fitted J types. Link to comment Share on other sites More sharing options...
Bazza Posted February 24, 2021 Author Report Share Posted February 24, 2021 2 hours ago, Pete Lewis said: this is from steves online manuals page 2.307 but looking at you pic the solenoid appears on the LH side so its a J type not a D type ??? the only change is a D type (sol on the RH side ) must have a relay the J type does not , but which ever the feed needs to be from a white ignition controlled wire certainly not off the ignition ballast coil wire the dropped voltage wont help the OD at all as the wiring goes up the hollow gear stick i would take a carefull lookas here it gets cooked and chafed try to get some silicon sheathed wire its more pliable/less chaffed and heat proofed Pete Sorry for the delay in reply, thought I had..... wire is from 12 volt side of ballast resistor. With the help of another member I have solved the issue. Thanks Barry Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 24, 2021 Report Share Posted February 24, 2021 so what was the solution we all want to know Pete Link to comment Share on other sites More sharing options...
Bazza Posted February 24, 2021 Author Report Share Posted February 24, 2021 28 minutes ago, Pete Lewis said: so what was the solution we all want to know Pete Hi Peter Colin very kindly provided a picture and explanation of how he’d wired his. So going to rewire utilising the reversing light circuit. With the current wiring set-up the solenoid on mine does click so I can only assume that this has always been the case. So now planning to clean out filters in the overdrive sump and hope that solves it. It also looks like has been a leak from the gearbox sump nut so lack of pressure/ not enough oil maybe a cause. If that doesn’t work.....back to the drawing boards 28 minutes ago, Pete Lewis said: so what was the solution we all want to know Pete Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 24, 2021 Report Share Posted February 24, 2021 J types can have a mind of their own if the 0 rings inside the solenoid are failing or stuck to remove the sol. you need a thin 1" af spanner dont use grips on the body if its tight it will wreck it the sol has 0 rings to seal its body but inside there is a small floating shuttle piston to get this out just remove the 10mm circlip in the end of the sol an shake the piston out it should be free and if shaken hear it rattle about while your in there its worth half an hour to have a look see Pete Link to comment Share on other sites More sharing options...
Bazza Posted February 24, 2021 Author Report Share Posted February 24, 2021 31 minutes ago, Pete Lewis said: J types can have a mind of their own if the 0 rings inside the solenoid are failing or stuck to remove the sol. you need a thin 1" af spanner dont use grips on the body if its tight it will wreck it the sol has 0 rings to seal its body but inside there is a small floating shuttle piston to get this out just remove the 10mm circlip in the end of the sol an shake the piston out it should be free and if shaken hear it rattle about while your in there its worth half an hour to have a look see Pete Thanks for the advice Pete.....just need to source a thin 1inch spanner.... Link to comment Share on other sites More sharing options...
Colin Lindsay Posted February 24, 2021 Report Share Posted February 24, 2021 Make one... we all end up doing it! Spanner and grinder combination. Some people buy ready-made versions but they're the kind of people who put mayonnaise on chips and that sort of thing. Wouldn't have chaps like that in my regiment. Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 24, 2021 Report Share Posted February 24, 2021 yes cut from a bit of tin plate its not overly tight but does seal on a copper washer a bit of oil will come out you will see the body is held on the base by small roll pins if you wrench it with grips it all comes apart Pete Link to comment Share on other sites More sharing options...
Peter Truman Posted February 24, 2021 Report Share Posted February 24, 2021 Colin I modified an old spanner as you suggest file the jaws and grind the thickness only issue is nowadays can I find it, no way where is it! Link to comment Share on other sites More sharing options...
thescrapman Posted February 24, 2021 Report Share Posted February 24, 2021 15 minutes ago, Peter Truman said: Colin I modified an old spanner as you suggest file the jaws and grind the thickness only issue is nowadays can I find it, no way where is it! In the tool chest with a large label tied to it saying "J-Type Spanner" Link to comment Share on other sites More sharing options...
Peter Truman Posted February 24, 2021 Report Share Posted February 24, 2021 No I have a separate small tool chest with special modified tools, ie brake spanner, sump spanner, thinned down ring spanner to fit Sprint carb to manifold nuts, 7/16in socket with thinned down outer end to fit a small space elsewhere on the Sprint, donut compressor to enable them to be fitted without dismantling the rear hub, but no J type spanner! Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 25, 2021 Report Share Posted February 25, 2021 the wifes got a small chest but dont see much of it these days Pete Link to comment Share on other sites More sharing options...
Colin Lindsay Posted February 25, 2021 Report Share Posted February 25, 2021 A socket wench? Link to comment Share on other sites More sharing options...
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